Door And Perimeter Duty Cycle Adjustments For Temperature Calibration; Door And Perimeter Heater Duty Cycle Automatic Control - NuAire NU-5800 Operation And Maintenance Manual

9.2 Door and Perimeter Duty Cycle adjustments for Temperature Calibration

The Door and Perimeter heaters are run on "Base Duty Cycle" calculations that is automatically increased or decreased to
run in accordance with the chamber temperature at a chosen set point. These duty cycles work in the controlled lab
environment but due to the many variables involved in temperature control there is also a manual adjustment. The heater
duty cycles can be adjusted to control condensation or to adjust the temperature uniformity in the chamber.
The inner glass door and outer shell perimeter temperature calibration is best accomplished by running the Incubator for
a minimum of 24 hours with the water pan in place and perform the following calibration sequence, if required. Open the
Incubator door and look for general condensation. Some condensation on the glass door can be desirable as an indication
of adequate humidity in the chamber. Typically, one to two inches of condensation in the corners of the glass door and/or
gasket indicates a properly calibrated door and perimeter heater. The perimeter heater is the heater located on the outer
shell next to the glass door gasket. If calibration is required, simply perform the procedure as stated below. The door and
perimeter heater operates as a base duty cycle calculated for the chamber temperature set point being used. In the door
and perimeter heater (adjustment) screen "100" = the calculated base duty cycle. Adjusting the value up or down adds or
removes 1 percent of the base duty cycle based on phase firing the control triac for that heater. Adjustments should be
limited to 5% up or down at a time.
The following steps should be taken for setting these duty cycle percentages:
•
Allow Incubator to stabilize at its given temperature and humidity level in run mode.
•
Enter the "Environmental Set Points" screen either from the MAIN SCREEN or the SYSTEM SETTINGS screen.
•
Select the numerical digits following the "Door" or "Perimeter" text.
•
Press ▲ or ▼ keys to increase or decrease the numerical value to the desired level.
•
Press "Done" to set current value and exit calibration.

9.2.1 Door and Perimeter heater duty cycle automatic control

The door and perimeter duty cycles are automatically reduced when the room temperature in the lab increases
enough to allow the contribution from these heaters to overheat the chamber. For example if the door and
perimeter duty cycles are set up when the room temperature is 22°C and the room temperature is allowed to
increase to 27°C. Less heat is required to keep the chamber at set point. If the chamber starts to overheat, the duty
cycles will be reduced at a rate of 1% per minute starting when the chamber temperature is 0.2°C above set point.
The duty cycles will continue to be reduced until the chamber temperature returns to set point. These duty cycles
are continuously monitored and will be increased slowly again, as long as the chamber temperature does not go over
the set point. If the room ambient reduces back to 22°C the door and perimeter duty cycles will actually be returned
to their original settings.
Note: If it is known that the lab room temperature where the Incubator is installed will vary significantly.
(For example, the heater or air conditioning is shut off after work hours or there is no air conditioning and
the room temperature has large temperature swings.)
The door and perimeter duty cycles should be set in the lower temperature expected in the lab.
Then the door and perimeter heaters will automatically be adjusted to avoid over temperature conditions in
the chamber when the room temperature rises.
In this case the chamber should be monitored for condensation regularly.
If the chamber walls and ceiling start to get excessive condensation the door and perimeter heater duty cycle
settings will need to be reduced.
OM0211
Rev 3 March 2013
Environmental Set-Points
Temperature Set-Point
CO2 Set-Point
Heaters, Door 100 Perimeter
Exit
Page 34 of 48
37.0C
5.0%
100